1. Field
The disclosure pertains to the technology of information displays, in particular to the liquid crystal displays (LCD), and could be utilized in devices of various configurations.
2. Description of the Related Art
The following references, which are incorporated by reference are of interest in this disclosure.
1. L. K. Vistrin. GVHO, 1983, vol. XXVII, 2nd ed., pp. 141-148
2. U.S. Pat. No. 5,007,942, 1991
3. RU 2120651, 1998
4. U.S. Pat. No. 5,739,296, 1998
These references are now further discussed.
There are liquid crystal (LC) displays, which are realized having two parallel flat plates, the inside surfaces of which are coated with patterns of optically transparent conducting material and the alignment layer. After the assembly of the plates the space between them is filled with liquid crystal, which forms a layer 5-20 μm thick and plays the role of the active medium, which changes its optical qualities (angle of twist of the polarizing plane) under the influence of electric field. The change in the optical qualities is registered in the cross-oriented polarizers, which are usually applied onto the inside surfaces of the plates. Therefore, the areas of the display, on the electrodes of which electrical field is not applied, will look bright (open state), while the areas, the electrodes of which are under the electrical field, will look dark (closed state) (L. K. Vistrin. GVHO, 1983, vol. XXVII, 2nd ed., pp. 141-148).
The main drawback of the described above displays is the limited viewing angle. This is because the multi-layered structure of the LC display is effectively controlled by the flux of light propagating towards the surface of the display within a limited solid angle. The polarizers in such displays are polymer-based, such as polyvinyl-alcohol, which is made optically anisotropic by uniform stretching of a thin film (U.S. Pat. No 5,007,942, 1991). The optical anisotropy is obtained as a result of ordering of the polymer molecules along the direction of stretching. When exposed to iodine vapor or iodine-containing solution or an organic dye, the film is colored with the intensity of color depending of the direction of the vector of the electric field E in the electromagnetic wave relative to the axis of stretching. Polarizing effectiveness of such films is determined by the concentration of iodine or other organic coloring agent and the degree of ordering of the polymer molecules. Such films feature the so-called positive dielectric anisotropy and positive dichroism. This means that the dipole moments of optical transition of molecules, which are responsible for absorption of light, are oriented along the direction of stretching. At the same time the ellipsoids of the angle dependence of the real and imaginary parts of the refraction coefficient have an extended form. Polarizers obtained from the described above films are termed O-type, since the “ordinary” wave will pass through, while the “extraordinary” will not.
Despite the high polarizing effectiveness, these polarizers have substantial drawbacks. These are low light and thermal resistance, large required thickness to achieve high effectiveness. One of the main drawbacks featured by the two cross-oriented polarizers is the high transmission of light incident at an angle (±45) to the surface of the polarizers.
There are LC displays that utilize polarizers on the inside surfaces of the glass plates (RU 2120651, 1998). The polarizers used in such displays are thin films with ordered molecular structure of the liquid crystal polarizer (LCP) (U.S. Pat. No. 5,739,296, 1998). The flat molecules of such LCP are grouped together into the so-called directionally ordered bunches—supramolecular complexes. The planes of the individual molecules, and thus their inherent dipole moments of optical transition, are oriented perpendicular to the axis of macroscopical orientation of the produced film. To create such structure one uses the liquid-crystalline state of the LCP, where the molecules are already ordered locally, while in one- or two-dimensional blocks oriented relative to each other. When applied onto a surface with an additional external alignment force, such substance assumes the macroscopical orientation, which upon dehydrating not only reins but could also improve on its own. The resulting axis of polarization is along the direction of the external aligning action. In this case the ellipsoids of the angle dependence of the real and imaginary parts of the refraction coefficient have disk-like shape.
The latter polarizers are termed E-type, since “extraordinary” wave is now transmitted and “ordinary” is blocked.
Such polarizer features a number of substantial disadvantages, which limit its applicability. One of those is the insufficient polarizing effectiveness, and some transmission of light has been registered through two parallel cross-oriented polarizers of this type with the incident unpolarized light at an angle to their surfaces. This effect is especially prominent when at least one of the polarizers has the diffused-reflection coating, which is used in the majority of LC displays.